My guess is that Ford won't come back and that they'll have to write Han as having died in the years since JEDI ended, but you never know...if Disney and Lucas dangle an enormous enough paycheck in front of Harrison's face anything's possible.
It's not like he's getting any good roles anymore aside from Indiana Jones, and the last one of those was four and a half years ago. He has nothing to lose really except his squeamishness about Star Wars
. There are times he reminds me of Shatner during the "Get a Life" period.